The present invention relates to gas chromatograph/mass spectrometer (GC/MS) systems, particularly to portable GC/MS systems, and more particularly to a mass spectrometer vacuum housing and pumping system.
Instruments which identify unknown chemical compounds using gas chromatograph/mass spectrometry are well known, as exemplified by U.S. Pat. No. 3,641,339 issued Feb. 8, 1972 to A. McCormick. In these early combined gas chromatography/mass spectrometry, the samples were generally carried from the chromatographic column to the mass spectrometer ion source in a carrier gas, usually helium, and the total ion current monitor of the mass spectrometer was used as the gas chromatograph detector. The limit of sensitivity was usually determined by the fluctuations of the carrier gas pressure in the mass spectrometer ion source. Such gas chromatograph/mass spectrometer (GC/MS) systems were large, heavy systems and generally located in laboratories or other research facilities, and thus unknown chemicals must be transported to such facilities for analysis. Such takes considerable time and expense compared to chemical analysis in the field or location of the unknown chemical. However, until recently, portable GC/MS systems were not available. Recent efforts to develop portable chemical analysis systems are exemplified by U.S. Pat. Nos. 4,888,295 issued Dec. 19, 1989 to S. Zaromb et al., and 5,153,433 issued Oct. 6, 1992 to B. D. Andresen et al.
U.S. Pat. No. 4,888,295 is directed to a portable system which includes a small, portable, low-pressure and low-power chromatographic analyzer and a chemical parameter mass spectrometry monitor including an array of sensors for detecting, identifying and measuring the concentrations of a variety of components in the eluent from the chromatographic analyzer. The monitor includes one or more operating condition controllers which may be used to change one or more of the operating conditions during exposure of the sensors to the eluent from the chromatography analyzer to form a response pattern which is then compared with a library of previously established patterns.
U.S. Pat. No. 5,153,433 utilizes a portable mass spectrometer having one or more adjustable electrostatic focusing sectors and an adjustable magnetic focusing sector, all of which are positioned inside a vacuum chamber through which the ion beam to be focused travels, and all of which may be adjusted via adjustment means accessible from outside the vacuum chamber. Mounting of the magnetic focusing sector, including the magnets used to focus the ion beam, entirely within the vacuum chamber, through which the ion beam to be focused travels, permits smaller magnets to be used, thus permitting reductions in both weight and bulk.
Commercially available portable or field deployable GC-MS systems, such as the Viking Spectra Trak, made by Viking Instruments, Reston, Va., are expensive, costing over $150,000 and weigh approximately 150 pounds, and utilize an existing commercial mass spectrometer vacuum system which requires dolly transport. Thus, the prior known portable systems are both expensive and difficult to take to the field because of size and weight thereof. In addition, the power consumption of the prior known portable systems, such as the above-referenced Viking Spectra Trak, is between 1,000 to 1,500 watts depending upon the operational mode. Also, there is a high atmospheric leak rate into the mass spectrometer (MS) vacuum housing due to casing porosity and the sealing method thereof.
The recent environment concerns and market has generated opportunities to widely utilize field deployable GC-MS systems. The critical need for a small portable chemical analysis instrument, which is easy to use in a field environment, but which provides laboratory-grade data, has generated much interest among potential users. The need for such instruments is worldwide in scope. The need is driven by the increasing public awareness of environmental issues, and secured by extensive and growing public policy and regulations impacting those issues. The following outlines various current and new future applications for high resolution portable GC-MS instruments:
1. Forensics: The support of law enforcement for the analysis of drugs, crime scene evidence, accident debris, and arson residues. PA1 2. Chemical Weapons and Treaty Monitoring: To assure compliance and the nonproliferation of chemical weapons, which require sensitive and specific analyses. PA1 3. Regional Transit Authorities: For fast response analysis of spills and accidents on the roadways. PA1 4. Environmental Laboratories: To provide an instrument which can be operated in the laboratory or quickly taken out into the field for special analysis projects. PA1 5. Medical and Hospital: Various diagnostic analysis of patients relative to drug overdose, poisoning, and illness which can be carried in ambulance and/or emergency rooms. PA1 6. Universities: Chemical analysis class work and research. PA1 7. Industries: Monitoring chemical wastes, production chemicals, assembly line quality control, and other manufacturing processes. PA1 8. Commercial and Military Airport Security: Looking for bombs (explosive vapors) and drugs (residues) in luggage or packages, and in cargo containers, etc.
More recently, in an effort to satisfy this need a lighter weight, portable high resolution GC/MS system has been developed for field organic chemical analysis with the sensitivity and specificity of a highly sophisticated laboratory GC/MS, and is described and claimed in U.S. application Ser. No. 08/225,111, filed Apr. 8, 1994, by B. D. Andresen et al., entitled "Portable Gas Chromatograph--Mass Spectrometer. This approach includes a conduction heated, forced air cooled small bore capillary gas chromatograph, a self-contained ion/sorption pump system, hydrogen supply, and a dual computer system used to control the hardware and acquire spectrum data, while weighing less than seventy pounds, requiring less than 600 watts of electric power at peak power, and can be incorporated in a 9.5.times.18.times.27 inch suitcase.
The portable Viking Instruments GC/MS referenced above, like many portable and laboratory units, employ the Hewlett-Packard mass spectrometer (MS) and its vacuum housing which consists of a cast aluminum housing with a large flat flange sealed with a flat rubber gasket. The vacuum systems for these units are typically based upon mechanical (i.e. turbomolecular) pumps. This combination results with a high atmospheric leak rate into the MS vacuum housing due to casting porosity of the aluminum housing and the sealing method. The mechanical vacuum pumps and control electronics are generally quite heavy, require a generous amount of electrical power, and, since they are high-speed rotational equipment, can fail during system movement.
Thus, there is a need for a readily portable, high resolution gas chromatograph/mass spectrometer (GC/MS) which eliminates the above-referenced leakage problems with commercially available GC/MS systems, and provides a minimum weight, portable system whereby the exact chemical characterization of unknown substances in the environment, at crime scenes, at accident sites, can be determined, or in an emergency room to aid the analysis of a poisonous substance. The present invention eliminates the above-referenced leakage problems, by providing a vacuum housing having cleaned and welded stainless steel tube and other components that are metal gasket sealed, and the vacuum pumps are small and light weight, require simple and minimal electrical controls, and use minimal electric power, which allow packaging into a small, light weight volume that will operate with minimal power requirements.